The fouling and cleaning of ultrafiltration membranes for black tea liquor clarification
Advancing the chemical engineering fundamentals
Filtration - II (T2-11b)
Keywords: Ultrafiltration, Black Tea, Fouling, Cleaning
P.J. Evans and M.R. Bird
Department of Chemical Engineering, University of Bath, UK.
A problem associated with the production of Ready To Drink (RTD) or iced tea is a phenomenon known as ‘tea creaming’, which gives the product a hazy or muddy appearance which can be detrimental to both appearance and taste. Membranes offer the possibility of producing a clarified liquor without the need for chemical addition or thermal processing, thus leading to a more natural product.
This paper reports experimental findings concerning the ultrafiltration of hot tea extract reconstituted from black tea powder. The filters studied were 10, 30 and 100kDa Fluoropolymer (FP) and Regenerated Cellulose (RC) ultrafiltration membranes. Colour, haze and stability of clarified permeate were analysed, and total solids determined. Theaflavin and caffeine content were measured using HPLC. Membranes were effective at producing a stable, clarified liquor at commercially viable fluxes.
An analysis of the changes in membrane surface properties through a complete fouling / cleaning cycle have been comprehensively studied. FTIR analysis demonstrates easy removal of tea species from RC membranes by NaOH cleaning whilst FP membranes remain coated with tea species after cleaning. The importance of roughness, hydrophobicity and surface charge are discussed for each membrane type through the fouling / cleaning cycles.
The adhesive force between model functional groups and the membrane surfaces is also reported. A stronger adhesion of model functional groups is seen to the FP membrane than to the RC membrane.
Fouling flux decline curves were fitted using a modified Hermia analysis to provide a mechanistic description of the fouling occurring under various processing conditions. Fouling mechanisms were found to be dominated by cake filtration.
Presented Tuesday 18, 09:25 to 09:45, in session Filtration - II (T2-11b).
